I think joomla uses a blowfish hash for passwords. There is a manual update to the webassist authentication that would allow you to set this up. You need to manually update the ->addFilter($filterColumn, $filterComparison, $filterType, $filterValue) method to use ->addHash($hashColumn, $hashComparison) instead after applying the server behavior.
I'm not positive that would work, but that is what I would try and I think there is a good chance it would.